Graphite-coated shaped body made of sintered silicon carbide

Abstract

Shaped body based on polycrystalline SiC and having a density of greater than 90% of its theoretical density and an adherent graphite layer on its surface, wherein the graphite layer is crystalline, has a thickness of 0.1-100 mum and has been produced by thermal surface decomposition of the SiC after it has been sintered to closed porosity.

What is claimed is:  
     
       1. A shaped body comprising 
       polycrystalline SiC having a surface and having a density of greater than 90% of theoretical density and an adherent layer consisting of graphite on said surface;  
       wherein the graphite layer is crystalline, has a thickness of 0.1-100 μm and has been produced by thermal surface decomposition of the SiC after it has been sintered to closed porosity.  
     
     
       2. A shaped body as claimed in  claim 1 , 
       wherein the graphite layer has a thickness in the range 0.5-20.0 μm.  
     
     
       3. A shaped body as claimed in  claim 1 , 
       wherein the graphite layer has a specific electrical resistance of from 0.5 to 5.0 mΩcm.  
     
     
       4. A shaped body as claimed in  claim 3 , 
       wherein the graphite layer has a specific electrical resistance of from 0.8 to 1.9 mΩcm.  
     
     
       5. A shaped body as claimed in  claim 1 , which comprises 
       70-99.7% by weight of SiC having an SiC crystallite size of from 1 to 2000 μm,  
       0.2-5.0% by weight of a substance selected from the group consisting of boron, boron compounds, Al, and Al compounds, and  
       0.1-25.0% by weight of additional carbon selected from the group consisting of amorphous carbon, graphite and mixtures thereof;  
       wherein the shaped body may have a total porosity of up to 10% by volume in the form of independent closed pores; and  
       all percents by weight are based upon the total weight of the shaped body.